The invention relates to flow control apparatus for the turbine of a turbocharger of an internal combustion engine.
DE-OS 28 43 202 already discloses an exhaust gas turbocharger for an internal combustion engine which has a radial turbine rotor surrounded by a spiral guide channel. Between the guide channel and the radial turbine wheel there is disposed an axially fixed annular partition, which has, distributed over its periphery, nozzle-like apertures which are inclined with respect to the tangential direction of the turbine rotor toward the axis of the turbine rotor. Around the annular partition there is disposed a diaphragm which is displaceable in the peripheral direction such that the cross-section of the nozzle-like apertures can be adjusted.
In addition, DE-AS 1 011 671 discloses an adjustable flow guide apparatus for a radial turbomachine wherein gases are fed via an adjustable guide grid to a turbine rotor (radial turbine). The adjustable guide grid consists of a plurality of guide vane rings of different dimensions and/or shapes, disposed one behind the other, and axially movable and manually adjustable.
Furthermore, DE-OS 26 33 587 discloses a tubular sliding device arranged between a dual-flow casing and a rotor of an exhaust gas turbocharger of an internal combustion engine. Regulation in the part-load range is achieved here by load-dependent closing of one flow passage. The highest permissible boost pressure is limited by a bypass slide valve.
U.S. Pat. No. 4,492,520 shows a gas turbine-driven motor vehicle having a radial turbine which is provided with an adjustable guide grid which has a plurality of guide vane rings of different configurations and whose axial adjustment can be effected in dependence on operating parameters of the engine.
With the known adjustable flow guide apparatus in the form of guide grids which do not permit to cover the vanes by means of a shield, a separate engine brake device must be installed because, with guide vane rings disposed axially behind one another, as disclosed in known prior art, a suitable throttle cross-section via positioning of the flow guide apparatus cannot be obtained.
In addition, adjustable flow guide apparatus of the known type, which are provided with guide vanes, have the disadvantage that only stepwise control of the approach flow direction with respect to the rotor is possible, so that optimum operation of the turbomachine can be achieved only at certain operating points. It is true that continuous control of mass flow by means of an azimuthally displaceable diaphragm mechanism is known, but such an arrangement complicates the design of the flow guide apparatus because of the larger number of movable parts.
It is the object of the invention to provide a flow guide apparatus for a turbocharger which is extremely simple in comparison with known flow apparatuses and yet does not have the above-mentioned disadvantages of the prior art.